The long range goal of these studies is to understand how the organization and physical properties of the mammalian sperm plasma membrane change with maturation in the epididymis and capacitation in the female tract, and how these modifications are related to important physiological alterations which occur in the male and female tracts, specifically the development of sperm motility, the acrosome reaction, and the potential to fertilize ova. Work from a number of laboratories on sperm from various mammalian species has shown that the sperm plasma membrane is highly organized, that different membrane components are localized in different regions of the membrane, and that this organization and localization changes with sperm maturation and capacitation (1-8). To effect this regionalization, the sperm must restrict or overcome the free random diffusion of their membrane components. In order to determine the nature of these restrictions to free diffusion and to understand how these restrictions change with maturation and capacitation, we propose to use fluorescence recovery after photobleaching, intensified video fluorescence microscopy, and rapid freeze deep etch electron microscopy to study changes in the ram sperm plasma membrane upon maturation and capacitation. Specifically we will address the following questions: 1. What are the restrictions to lipid and protein diffusion which lead to the localized distributions of these membrane components on mammalian spermatozoa 2. How do the diffusibility of sperm membrane lipids and protein change during maturation and capacitation 3. What is the nature of the processes which result in the redistribution of membrane components during maturation and capacitation 4. To what extent does motility and hyperactivated motility control the distribution and redistribution of membrane components